Human exposure to chemicals is rarely limited to one single chemical. Recent concern about groundwater contamination in agricultural areas has led the NTP to initiate a study of the toxicology of pesticide/fertilizer chemical mixtures which are based on confirmed groundwater contamination in California and Iowa. While the long-term toxicity studies were being done on contract, specific myelotoxicity aid residual effects of bone marrow were investigated. Bone marrow parameters were monitored in mice exposed to 0, 1X, 10X, and 100X of chemical mixture II or III drinking water for 13 weeks. Both chemical mixture II and III had no significant effect compared to the control group on bone marrow cellularity or granulocyte macrophage progenitors in female B6C3F1 mice as all the concentrations tested.